Light emitting diode and method for manufacturing the same

ABSTRACT

A light emitting diode includes a substrate, a first-type semiconductor layer, a nanorod layer and a transparent planar layer. The first-type semiconductor layer is disposed over the substrate. The nanorod layer is formed on the first-type semiconductor layer. The nanorod layer includes a plurality of nanorods and each of the nanorods has a quantum well structure and a second-type semiconductor layer. The quantum well structure is in contact with the first-type semiconductor layer, and the second-type semiconductor layer is formed on the quantum well structure. The transparent planar layer is filled between the nanorods. A surface of the second-type semiconductor layer is exposed out of the transparent planar layer.

RELATED APPLICATIONS

This application claims priority to Taiwan Application Serial Number101122831, filed Jun. 26, 2012, the contents of which are hereinincorporated by reference in their entireties.

BACKGROUND

1. Technical Field

The present invention relates to a light emitting diode and a method formanufacturing the light emitting diode. More particularly, the presentinvention relates to a light emitting diode having a number of nanorodsand a method for manufacturing the light emitting diode.

2. Description of Related Art

There has been rapid progress in light emitting technologies in recentyears, and high luminous efficiency and low power consumption arerequired for light emitting devices. Among the various types of lightemitting technologies, much attention has been given to light emittingdiode (LED). LEDs are advantageous in high luminous efficiency, fastresponse time, long lifespan and mercury free. Furthermore, LEDs aresmall in size, and provide high color gamut as well as high resistanceto external impact. Therefore, LEDs gradually replace conventional lightemitting devices. LEDs have been applied in various fields due to itssignificant progress, and it seems to become the major light source for21^(st) century. In view of the application of light sources, onecritical specification parameter is the light-emitting efficiency, andtherefore many researchers commit to increase the light-emittingefficiency of LEDs.

SUMMARY

According to one aspect of the present disclosure, a light emittingdiode is provided. The light emitting diode includes a substrate, afirst-type semiconductor layer, a nanorod layer and a transparent planarlayer. The first-type semiconductor layer is disposed over thesubstrate. The nanorod layer is formed on the first-type semiconductorlayer. The nanorod layer includes a plurality of nanorods and each ofthe nanorods has a quantum well structure and a second-typesemiconductor layer. The quantum well structure is in contact with thefirst-type semiconductor layer, and the second-type semiconductor layeris formed on the quantum well structure. The transparent planar layer isfilled between the nanorods, in which a surface of the second-typesemiconductor layer is exposed out of the transparent planar layer.

According to one embodiment of the present disclosure, the transparentplanar layer is made of an insulating material comprisingbenzocyclobutene (BCB).

According to one embodiment of the present disclosure, the quantum wellstructure has a width W and a height H, and the width W and the height Hsatisfy the following formula (I):

0.5 H≦W<10 H  formula (I).

According to one embodiment of the present disclosure, the width W issubstantially equal to the height H.

According to one embodiment of the present disclosure, the height H isabout 5 nm to about 50 nm.

According to one embodiment of the present disclosure, a spacinginterval between any two adjacent nanorods is about 2 nm to about 3 nm.

According to one embodiment of the present disclosure, the lightemitting diode further includes a transparent electrode layer thatcovers the transparent planar layer and a top portion of each of thesecond-type semiconductor layers.

According to one embodiment of the present disclosure, the lightemitting diode may further include a first type contact pad and a secondtype contact pad. The first type contact pad is disposed on thefirst-type semiconductor layer. The second type contact pad is disposedon the transparent electrode layer.

According to one embodiment of the present disclosure, the first-typesemiconductor layer comprises a N-type gallium nitride layer. Each ofthe quantum well structures includes a multiple quantum well structure.Each of the second-type semiconductor layers includes P-type galliumnitride.

According to one embodiment of the present disclosure, the lightemitting diode may further include an undoped gallium nitride layer, andthe undoped gallium nitride layer is disposed between the first-typesemiconductor layer and the substrate.

According to one embodiment of the present disclosure, the first-typesemiconductor layer, the nanorod layer and the transparent planar layerconstitute a trapezoid sidewall structure.

According to one embodiment of the present disclosure, the trapezoidsidewall structure has an oblique plane that forms an included angle ofabout 30 degrees to about 150 degrees with the substrate.

According to one aspect of the present disclosure, a method formanufacturing a light emitting diode is provided. The method includesthe steps of: providing a substrate; forming a first-type semiconductorlayer on the substrate; forming a quantum well layer on the first-typesemiconductor layer; forming a second-type semiconductor layer on thequantum well layer; patterning the quantum well layer and thesecond-type semiconductor layer to form a plurality of nanorods; fillinga transparent planar material into a space between the nanorods, inwhich a top portion of each of the nanorods is exposed out of thetransparent planar material; and forming a transparent electrode layerto cover the transparent planar material and the top portion.

According to one embodiment of the present disclosure, the step ofpatterning the quantum well layer and the second-type semiconductorlayer includes a step of forming a quantum well structure in each of thenanorods. Each of the quantum well structure has a width W and a heightH, and the width W and the height H satisfy the following formula (I):

0.5 H≦W<10 H  formula (I).

According to one embodiment of the present disclosure, the step ofpatterning the quantum well layer and the second-type semiconductorlayer includes the steps of: forming a patterned hard mask on thesecond-type semiconductor layer, in which a portion of the second-typesemiconductor layer is exposed; removing the exposed portion of thesecond-type semiconductor layer and the quantum well layer there underto form the nanorods; and removing the patterned hard mask on thenanorods.

According to one embodiment of the present disclosure, the step offiling the transparent planar material includes filling benzocyclobuteneinto the space between the nanorods.

According to one embodiment of the present disclosure, the method mayfurther include removing a portion of the second-type semiconductorlayer, a part of the nanorods, a portion of the first-type semiconductorlayer and a portion of the transparent planar material to form atrapezoid sidewall structure such that a portion of the first-typesemiconductor layer is exposed.

According to one embodiment of the present disclosure, the method mayfurther include a step of forming a first connecting pad and a secondconnecting pad respectively on the transparent electrode layer and theexposed portion of the first-type semiconductor layer.

According to one embodiment of the present disclosure, the first-typesemiconductor layer includes N-type gallium nitride, and the second-typesemiconductor layer includes P-type gallium nitride.

According to one embodiment of the present disclosure, the method mayfurther include a step of forming an undoped gallium nitride layer onthe substrate prior to forming the first-type semiconductor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the followingdetailed description of the embodiments, with reference made to theaccompanying drawings as follows:

FIG. 1A is a cross-sectional view schematically illustrating a lightemitting diode according to one embodiment of the present disclosure;

FIG. 1B is a cross-sectional view schematically illustrating nanorodsaccording to one embodiment of the present disclosure;

FIG. 2 is a flow chart showing a method for manufacturing a lightemitting diode according to one embodiment of the present disclosure;

FIGS. 3A-3E are cross-sectional views illustrating the process steps ofthe method illustrated in FIG. 2; and

FIG. 4 is a graph showing the relationship between the internal quantumefficiency (η) of the light emitting diode and the ratio of the width tothe height (W/H) of the quantum well structure according to oneembodiment of the present disclosure.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the disclosed embodiments. It will be apparent,however, that one or more embodiments may be practiced without thesespecific details. In other instances, well-known structures and devicesare schematically shown in order to simplify the drawings.

According to one aspect of the present disclosure, a light emittingdiode and a method for manufacturing the light emitting diode aredisclosed. The following disclosure provides many different embodiments,or examples, for implementing different features of the invention.Specific examples of components and arrangements are described below.These are, of course, merely examples and are not intended to belimiting. For example, the formation of a first layer over or on asecond layer in the description that follows may include embodiments inwhich the first and second layers are formed in direct contact, and mayalso include embodiments in which additional layers may be formedbetween the first and second layers, such that the first and secondfeatures may not be in direct contact. In addition, the presentdisclosure may repeat reference numerals and/or letters in the variousexamples. This repetition is for the purpose of simplicity and clarityand does not in itself dictate a relationship between the variousembodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. For example, if the device in the figures is turned over,elements described as being “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the exemplary term “below” can encompass both an orientation ofabove and below. The apparatus may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein may likewise be interpreted accordingly.

FIG. 1A is a cross-sectional view schematically illustrating a lightemitting diode 100 according to one embodiment of the presentdisclosure. The light emitting diode 100 includes a substrate 110, afirst-type semiconductor layer 120, a nanorod layer 130 and atransparent planar layer 140.

The substrate 110 is configured to support structures formed thereon,and to provide a surface required for growing an epitaxial layer. Thesubstrate 110 may be a sapphire substrate, a silicon carbide (SiC)substrate, a gallium nitride substrate, a zinc oxide (ZnO) substrate ora silicon substrate, for example.

The first-type semiconductor layer 120 is disposed over the substrate110. The first-type semiconductor layer 120 may be an N-type galliumnitride layer, for example.

In one embodiment, the light emitting diode 100 may optionally includesan undoped gallium nitride layer 114 positioned between the first-typesemiconductor layer 120 and the substrate 110. The undoped galliumnitride layer 114 may be configured as a buffer layer between thesubstrate 110 and the first-type semiconductor layer 120.

The nanorod layer 130 is formed on the first-type semiconductor layer120. The nanorod layer 130 includes a plurality of nanorods 132, whichstand erect on the first-type semiconductor layer 120. FIG. 1B is across-sectional view schematically illustrating the nanorod 132according to one embodiment of the present disclosure. As depicted inFIG. 1B, each of the nanorod 132 includes a second-type semiconductorlayer 134 a and a quantum well structure 134 b. The quantum wellstructure 134 b is in contact with the first-type semiconductor layer120, and the second-type semiconductor layer 134 a is formed on thequantum well structure 134 b. In examples, the quantum well structure134 b may be a multiple quantum well structure, and the second-typesemiconductor layer 134 a may be a P-type gallium nitride layer. In oneembodiment, the spacing interval D between any two adjacent nanorods 132is about 2 nm to about 3 nm.

In another embodiment, the quantum well structure 134 b has a width Wand a height H. The width W and the height H satisfy the followingformula (I):

0.5H≦W<10 H  formula (I).

In other words, the width W of the quantum well structure 134 b isgreater than or equal to 0.5 fold of the height H of the quantum wellstructure 134 b, but the width W of the quantum well structure 134 b isless than 10 folds of the height H of the quantum well structure 134 b.That is, the ratio of the width W to the height H (W/H) is greater thanor equal to 0.5, but less than 10.

In this embodiment, the aforementioned relationship between the width Wand the height H provides a significant effect on the internal quantumefficiency. FIG. 4 is a graph showing the relationship between theinternal quantum efficiency (r₁) of the light emitting diode and theratio of the width to the height (W/H) of the quantum well structure 134b, according to one embodiment of the present disclosure. When the ratioof the width W to the height H (W/H) of the quantum well structure 134 bis greater than 10, the internal quantum efficiency η is about 60%.Significantly, when the ratio of W/H is less than 10, the internalquantum efficiency η dramatically increases. When the ratio of W/H isless than 1.5, the internal quantum efficiency η is significantly raisedto a level of about 90%. Therefore, according to one embodiment of thepresent disclosure, the ratio of W/H is about 0.8 to about 1.5,preferably the width W substantially equal to the height H. In onespecific example, the height H is about 5 nm to about 50 nm.

Accordingly, the light-emitting efficiency of the light emitting diodemay be significantly increased according to the embodiments of thepresent disclosure.

The transparent planar layer 140 is filled in the void space between thenanorods 132. It is noted that the top portion of each of the nanorods132 is exposed out of the transparent planar layer 140. In particular,the top surface of the second-type semiconductor layer 134 a is exposedout of the transparent planar layer 140. In other words, the transparentplanar layer 140 substantially encircles and covers the sidewall of eachof the nanorods 132, but the transparent planar layer 140 does not coverthe top portions of the nanorods 132. In one embodiment, transparentplanar layer 140 is made of an insulating material comprisingbenzocyclobutene (BCB). The benzocyclobutene exhibits excellentflowability and planarization avail, so that the tiny space between thenanorods 132 may be well filled with benzocyclobutene material, withoutbubbles formed therein. Moreover, the transparent planar layer 140 mayprotect the nanorods 132 from damage due to external impact.

In one embodiment, the light emitting diode 100 may further include atransparent electrode layer 150, a first type contact pad 161 and asecond type contact pad 162. The transparent electrode layer 150 coversthe transparent planar layer 140 and the top portion of the second-typesemiconductor layer 134 a. The transparent electrode layer 150 is incontact with the second-type semiconductor layer 134 a, so that thetransparent electrode layer 150 may be electrically connected to thefirst-type semiconductor layer 120 through the nanorods 132. Inaddition, the first type contact pad 161 is disposed on the first-typesemiconductor layer 120, whereas the second type contact pad 162 isdisposed on the transparent electrode layer 150. The first and secondtype contact pads 161, 162 may be used to electrically connect to apower supply or an electrical circuit.

In another embodiment, the first-type semiconductor layer 120, thenanorod layer 130 and the transparent planar layer 140 constitute atrapezoid sidewall structure 170 of the light emitting diode 100, asdepicted in FIG. 1A. Specifically, the trapezoid sidewall structure 170may include an oblique plane, which forms an included angle α with thetop surface of the substrate 110. The included angle α, for example,ranges from about 30 degrees to about 150 degrees. The formation of thetrapezoid sidewall structure 170 may increase the light-extractionefficiency of the light emitting diode 100.

According to another aspect of the present disclosure, a method formanufacturing a light emitting diode is provided. FIG. 2 is a flow chartshowing a method 200 for manufacturing a light emitting diode accordingto one embodiment of the present disclosure. The method 200 at leastincludes step 210 to step 270. FIGS. 3A-3E are cross-sectional viewsillustrating the process steps of the method 200 illustrated in FIG. 2.

In step 210, a substrate 310 is provided, as depicted in FIG. 3A. Thesubstrate 310 may be a sapphire substrate, a silicon carbide (SiC)substrate, a gallium nitride substrate, a zinc oxide (ZnO) substrate ora silicon substrate, for example.

In step 220, a first-type semiconductor layer 320 is formed over thesubstrate 310, as depicted in FIG. 3A. For instance, the first-typesemiconductor layer 320 may be formed by hydride vapor phase epitaxyprocesses, metal organic chemical vapor deposition processes ormolecular beam epitaxy processes. In examples, the first-typesemiconductor layer 320 may be a semiconductor layer that comprisesN-type gallium nitride.

After step 210, but prior to step 220, an undoped gallium nitride layer314 may optionally be formed on the substrate 310, as illustrated inFIG. 3A. The undoped gallium nitride layer 314 may be configured as abuffer layer between the substrate 310 and the first-type semiconductorlayer 320.

In step 230, a quantum well layer 330 is formed on the first-typesemiconductor layer 320, as depicted in FIG. 3A. For instance, thequantum well layer 330 may be a multiple quantum well layer.

In step 240, a second-type semiconductor layer 340 is formed on thequantum well layer 330. For instance, the second-type semiconductorlayer 340 may be formed by hydride vapor phase epitaxy processes, metalorganic chemical vapor deposition processes or molecular beam epitaxyprocesses. In examples, the second-type semiconductor layer 340 may be asemiconductor layer that comprises P-type gallium nitride.

In step 250, both the quantum well layer 330 and the second-typesemiconductor layer 340 are patterned to form a plurality of nanorods350, as depicted in FIG. 3C. In one embodiment, the quantum well layer330 and the second-type semiconductor layer 340 are patterned throughthe method described below. As depicted in FIG. 3B, a patterned hardmask 342 is formed on the second-type semiconductor layer 340. A portionof the second-type semiconductor layer 340 is exposed, in which theexposed portion is not covered by the patterned hard mask 342.Subsequently, the exposed portion of the second-type semiconductor layer340 and the quantum well layer 330 there under are removed to form thenanorods 350. In particular, conventional dry etching techniques may beemployed to etch the quantum well layer 330 and the second-typesemiconductor layer 340. Thereafter, the patterned hard mask 342 on thenanorods 350 is removed and the structure shown in FIG. 3C is obtained.Accordingly, a void space S is formed between these nanorods 350 suchthat the nanorods 350 are spaced apart from each other. Each of thenanorods 350 includes a portion of the quantum well layer 330 and aportion of the second-type semiconductor layer 340. In one example, eachof the nanorods 350 has a substantially identical width, in which thewidth of the top portion of each nanorod 350 substantially equals thewidth of the bottom portion of said nanorod 350.

In one embodiment, the step 250 of patterning the quantum well layer 330and the second-type semiconductor layer 340 includes forming a quantumwell structure 134 b (shown in FIG. 1B) in each of the nanorods, andeach quantum well structure 134 b has a width W and a height H thatsatisfy the following formula (I):

0.5H≦W<10 H  formula (I).

In this embodiment, the height H of the quantum well structure 134 b isequal to the thickness of the quantum well layer 330. Accordingly, thestep of patterning the quantum well layer 330 and the second-typesemiconductor layer 340 has to take account of the thickness of thequantum well layer 330 formed in the step 230 such that the width of thequantum well structure 134 b may satisfy formula (I).

In step 260, a transparent planar material 360 is filled into the voidspace between the nanorods 350, as depicted in FIG. 3D. The top portion350T of each of the nanorods 350 is exposed out of the transparentplanar material 360. In one example, the step of filling the transparentplanar material 360 includes filling benzocyclobutene into the voidspace between the nanorods 350. In other words, the transparent planarmaterial 360 may include benzocyclobutene.

In step 270, a transparent electrode layer 370 is formed to cover thetransparent planar material 360 and the top portion 350T of each of thenanorods, as depicted in FIG. 3E. In particular, the transparentelectrode layer 370 is in contact with each of the nanorods 350 so thatthe transparent electrode layer 370 may be electrically connected to thefirst-type semiconductor layer 320 through the nanorods 350.

In one embodiment, after the step 270, the method 200 may optionallyincludes removing a portion of the second-type semiconductor layer 340,a part of the nanorods 350, a portion of the first-type semiconductorlayer 320 and a portion of the transparent planar material 360 to form atrapezoid sidewall structure 380, as depicted in FIG. 3E. The trapezoidsidewall structure 380 may include an oblique plane, which forms anincluded angle of about 30 degrees to about 150 degrees with the topsurface of the substrate. In the step of forming the trapezoid sidewallstructure 380, another portion of the first-type semiconductor layer 320is exposed.

In another embodiment, after forming the trapezoid sidewall structure380, the method 200 may optionally include forming a first connectingpad 391 and a second connecting pad 392 respectively on the transparentelectrode layer 370 and the exposed portion of the first-typesemiconductor layer 320, as depicted in FIG. 3E.

According to the method disclosed herein, a number of nanorods areformed in the light emitting diode, and more significantly the dimensionof each of the nanorods is excellently uniform. In addition, the methoddisclosed herein is suitable for large-area production of light emittingdiodes with nanorods.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims.

What is claimed is:
 1. A light emitting diode, comprising: a substrate;a first-type semiconductor layer disposed over the substrate; a nanorodlayer formed on the first-type semiconductor layer, the nanorod layerincluding a plurality of nanorods and each of the nanorods including aquantum well structure and a second-type semiconductor layer, whereinthe quantum well structure is in contact with the first-typesemiconductor layer, and the second-type semiconductor layer is formedon the quantum well structure; and a transparent planar layer filledbetween the nanorods, wherein a surface of the second-type semiconductorlayer is exposed out of the transparent planar layer.
 2. The lightemitting diode according to claim 1, wherein the transparent planarlayer is made of an insulating material comprising benzocyclobutene(BCB).
 3. The light emitting diode according to claim 1, wherein thequantum well structure has a width W and a height H, and the width W andthe height H satisfy the following formula (I):0.5 H≦W<10 H  formula (I).
 4. The light emitting diode according toclaim 3, wherein the width W is substantially equal to the height H. 5.The light emitting diode according to claim 4, wherein the height H isabout 5 nm to about 50 nm.
 6. The light emitting diode according toclaim 1, wherein a spacing interval between any two adjacent nanorods isabout 2 nm to about 3 nm.
 7. The light emitting diode according to claim1, further comprising a transparent electrode layer that covers thetransparent planar layer and a top portion of each of the second-typesemiconductor layers.
 8. The light emitting diode according to claim 7,further comprising: a first type contact pad disposed on the first-typesemiconductor layer; and a second type contact pad disposed on thetransparent electrode layer.
 9. The light emitting diode according toclaim 1, wherein the first-type semiconductor layer comprises a N-typegallium nitride layer, each of the quantum well structures comprises amultiple quantum well structure, and each of the second-typesemiconductor layers comprises P-type gallium nitride.
 10. The lightemitting diode according to claim 1, further comprising an undopedgallium nitride layer, and the undoped gallium nitride layer is disposedbetween the first-type semiconductor layer and the substrate.
 11. Thelight emitting diode according to claim 1, wherein the first-typesemiconductor layer, the nanorod layer and the transparent planar layerconstitute a trapezoid sidewall structure.
 12. The light emitting diodeaccording to claim 11, wherein the trapezoid sidewall structure has anoblique plane that forms an included angle of about 30 degrees to about150 degrees with the substrate.
 13. A method for manufacturing a lightemitting diode, comprising: providing a substrate; forming a first-typesemiconductor layer on the substrate; forming a quantum well layer onthe first-type semiconductor layer; forming a second-type semiconductorlayer on the quantum well layer; patterning the quantum well layer andthe second-type semiconductor layer to form a plurality of nanorods;filling a transparent planar material into a space between the nanorods,wherein a top portion of each of the nanorods is exposed out of thetransparent planar material; and forming a transparent electrode layerto cover the transparent planar material and the top portion.
 14. Themethod according to claim 13, wherein the step of patterning the quantumwell layer and the second-type semiconductor layer comprising: forming aquantum well structure in each of the nanorods, wherein each of thequantum well structure has a width W and a height H, and the width W andthe height H satisfy the following formula (I):0.5 H≦W<10 H  formula (I).
 15. The method according to claim 14, whereinthe step of patterning the quantum well layer and the second-typesemiconductor layer comprising: forming a patterned hard mask on thesecond-type semiconductor layer, wherein a portion of the second-typesemiconductor layer is exposed; removing the exposed portion of thesecond-type semiconductor layer and the quantum well layer there underto form the nanorods; and removing the patterned hard mask on thenanorods.
 16. The method according to claim 15, wherein the step offiling the transparent planar material comprises fillingbenzocyclobutene into the space between the nanorods.
 17. The methodaccording to claim 16, further comprising: removing a portion of thesecond-type semiconductor layer, a part of the nanorods, a portion ofthe first-type semiconductor layer and a portion of the transparentplanar material to form a trapezoid sidewall structure such that aportion of the first-type semiconductor layer is exposed.
 18. The methodaccording to claim 17, further comprising a step of forming a firstconnecting pad and a second connecting pad respectively on thetransparent electrode layer and the exposed portion of the first-typesemiconductor layer.
 19. The method according to claim 18, wherein thefirst-type semiconductor layer comprises N-type gallium nitride, and thesecond-type semiconductor layer comprises P-type gallium nitride. 20.The method according to claim 19, further comprising a step of formingan undoped gallium nitride layer on the substrate prior to forming thefirst-type semiconductor layer.